Well done in losing the excess feller..... keep doing so and that will ease the stress on your joints..... just listen and don't kill yourself.....
Improve your muscle tissue with either light weight training and/or a mixture of isotonic/isometric exercise and light weights..... when your joint issue is ok train squats gradually until you can do 100 with comfort....never rush it and start with what you can do comfortably...... add a little more each time.

At 55 still do this regularly with fast walking for aerobic exercise or a bicycle if you have one....